250 
hence a part either of the middle or the lateral one of the three walls 
that I have here described in fishes. To the free ventral edge of this 
cartilage, in Echidna, the membrana spheno-obturatoria of Gaupr’s 
descriptions has its attachment, this membrane and the ala tempo- 
ralis of Gaupp’s descriptions forming the lateral wall and the floor 
of the cavum epiptericum. This latter cavity is traversed by a venous 
vessel that is called, in the anterior part of its course through the 
cavity, the sinus cavernosus, and it is said to receive one branch 
coming from the orbit and another from the cranial cavity, the latter 
vessel being a large one that lies anterior to the hypophysis and issues 
from the cranial cavity through the fissura pseudooptica. The latter 
vessel evidently corresponds to the pituitary vein of my descriptions 
of fishes, but its foramen of exit from the cranial cavity les relatively 
far forward, approximately in the position of the pituitary foramen 
in Lepidosteus instead of that of the corresponding foramen in 
selachians, and it has furthermore fused with the foramina for the 
nervi opticus and oculomotorius. Posteriorly, the sinus cavernosus 
of Echidna is said to be jomed both by the sinus transversus, which 
comes from the dorsal portion of the cranial cavity, and the sinus 
petrobasilaris, which comes from the posterior portion of the cranial 
cavity, the vessel so formed then being called the vena capitis lateralis. 
This latter vein is then said by Gavpp (I. c. p. 598) to issue from the 
cranial cavity (Schädelraum) through the hindermost corner of the 
fenestra spheno-parietalis. This would however seem to be a misinter- 
pretation of the conditions, for the sinus cavernosus is nowhere said 
to have left the cavum epiptericum, through the fenestra spheno- 
parietalis, to enter the cranial cavity proper; and, furthermore, if 
this sinus is the homologue of a certain section of the internal jugular 
vein of fishes, which seems certain, it must always le, morphologi- 
cally, external to the fenestra spheno-parietalis, which fenestra is 
said by Gaupp to lie in the plane of the primitive lateral wall of the 
chondrocranium. It seems therefore probable that the sinus petro- 
basilaris traverses, morphologically, the fenestra spheno-parietalis 
to fall into the sinus cavernosus, and that the vena capitis lateralis, 
lying always morphologically in the cavum epiptericum, simply issues 
from that cavum along the lateral edge of the hindermost corner of 
the fenestra spheno-parietalis, between that edge and the hind edge 
of the membrana spheno-obturatoria. But however this may be, 
the vena capitis lateralis, having issued from the cavum epiptericum 
i 
